Pipe Diameter Inconsistency

Has anyone run into the issue that the Pipe command does not always result in a consistent pipe diameter?

See example file. When the input curve was closed, the pipe’s diameter varied. If even the curve was broken slightly, the pipe’s diameter was consistent.

Is it a bug or am I using an incorrect setting?

PipeNonConsistentDiameter.3dm (757.4 KB)

This seems to be a function of the Pipe option “Fit Rail” yes or no. If I do not want to refit the rail but want to use the original curve, is Rhino be unable to give a consistent diameter?